What to expect if FreeNAS loses connection to disk shelf?

Discussion in 'FreeBSD and FreeNAS' started by Cape, Jan 12, 2019 at 9:34 AM.

  1. Cape

    Cape New Member

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    I just set up a FreeNAS VM to start experimenting with. VM on ESXi, passthrough of a LSI9200, connected to external disk shelf.
    I figured it would be a good thing to know what would happen if my disk shelf lost power or similar, so I powered it down. This led to two unexpected things:
    1. It took > 1 minute until FreeNAS seemed to notice (pop an alert in the UI, that is)
    2. After it noticed, a lot of things seem to die. The UI no longer works, ssh doesn't work, and even console login stalls after giving the password.

    Is this actually expected behavior, or something likely to be wrong with my install?
     
    #1
  2. NathanM3

    NathanM3 New Member

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    I had this same issue a couple weeks ago. What I found was that freenas was using swap. Freenas uses a 2gb partition on the pool drives for swap. So when the pool drives got disconnected, the swap partition that freenas was using also got disconnected.

    There is a system tunable to adjust the amount of ram the ZFS leaves free. I adjusted this so that more ram is left free and I have not seen it swap since. This system has about 100gb of ram, so it was not caused by a lack of sufficient hardware.

    I did not test whether this completely fixes the crashing problem when disconnecting drives, but it fixed the root cause that I saw. The system is in production so I didn't test it further.
     
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    Last edited: Jan 12, 2019 at 10:43 AM
  3. Cape

    Cape New Member

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    Oh, yeah, that would cause problems. This system probably hadn't swapped very much either, but I would expect it to be somewhat confused anyway if swap space goes away without notice.
    Still, seems a bit fragile - I noticed FreeNAS will by default (and with strict warnings about not disabling it) add some swap on all pools, and if it crashes the entire system if it loses any of those? Otherwise I'd have just added another non-external disk as swap space.
     
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